Spectral data was obtained with SF-56A spectrophotometer in the 370 - 770 nm range, 1 nm step in Moscow State University Gemological Center. Spectra were recorded through two opposite parallel windows of the sample in room temperature.

All spectral data recorded on the spectrometer were converted into an adsorption coefficient in mm-1 taking into consideration the thickness of the sample and the refraction coefficient of the gem material. All spectral data for natural (untreated) colored diamonds was averaged with 20 nm step.

A Prism model with similar thickness as used for spectral data collection was selected in DiamCalc (for polished stones - Helium scanned 3D model of radiant cut). Light conditions for the prism in DiamCalc files: one transmitted source type A (for polished stones 3D models: the standard Dialite DiamCalc lighting).

Corresponding absorption spectra used for modeling are available in the Microsoft
Excel format.

Corundum Orange Red direction 2
Spectrum of the same material obtained through the 11.5 mm thick plate along another direction. Cr3+ features also present in spectrum of this stone, but the concentration of Cr is much lower.

Diamond Dark Orange BrownA dark orange-brown natural diamond (untreated) spectrum obtained through 3.6 mm thick plate. This diamond is Ia type and it can be assumed that its color is connected with dislocations.

Quartz through the zone with more yellow colorSpectrum of the same material obtained through the same plate but through the zone with more yellow color. Color of that stone is related with Fe3+ presence.